Ink, and ink-jet recording method and apparatus employing the ink

ABSTRACT

An ink including a recording agent and a liquid medium for dissolution or dispersion thereof, the recording agent being a compound represented by the general formula ##STR1## wherein R 1  and R 2  are respectively a radical selected from the group of lower alkyl, lower alkoxy, --NHCOCH 3 , --COOM, and --SO 3  M; R 3 , R 4 , and R 5  are respectively a radical selected from the group of hydrogen, hydroxyl, lower alkyl, lower alkoxy, amino, --SO 3  M, and --COOM; A is ##STR2## R 6  and R 7  are respectively a radical selected from the group of hydrogen, hydroxyl, and lower alkoxy; m is 1 or 2; n is 0 or 1; and M is alkali metal or ammonium.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ink, an ink-jet recording methodemploying the ink, and an apparatus employing the ink. Moreparticularly, the present invention relates to a recording liquid whichprovides high density and water resistance of printed letters onnon-coated paper such as wood-free paper, paper for copying, bond paper,paper for reporting, and the like, and which provides improved indoordiscoloration of an image recorded on coated paper having animage-receiving layer thereon composed of a binder and a pigment. Thepresent invention also relates to an ink-jet recording method, anink-jet recording unit, an ink-jet recording apparatus, and an inkcartridge.

2. Related Background Art

Heretofore, aqueous inks having a water-soluble dye dissolved in anaqueous medium have been used for ink-jet recording. The inks for such ause are required to have properties as below:

(1) providing sufficient density of images,

(2) having satisfactory drying property on recording mediums,

(3) causing little feathering or running of images,

(4) causing no flowing-out of the recorded images when brought intocontact with water, alcohol, or the like, or allowing satisfactorydecipherment even when some flowing out occurs (water-resistance),

(5) providing high light-fastness of recorded images,

(6) causing no clogging of a tip of a pen or a nozzle,

(7) causing no inconvenience in printed images such as blurring andscratching in continuous recording or at the re-start of recording aftera long term of intermission of the recording (ejection stability),

(8) being stable during storage,

(9) causing no problem on contact with a constituting member of arecording means on use,

(10) giving no hazard to an operator,

and so forth.

Furthermore, in an ink-jet recording system, utilizing thermal energy,the property below is required in addition to the above requirements:

(11) having high heat resistance, and giving no adverse influence to athermal energy-generating means.

As a specific example of the dye, C.I. Food Black 2 is mainly used inink-jet recording for both mono-color and full-color images (seeJapanese Patent Application Laid-Open Nos. 59-93766, and 59-93768).

An ink using C.I. Food Black 2 is satisfactory in density of recordedimages, but still involves problems on light-fastness andwater-resistance of recorded images: such that the black color turnsbrown on prolonged light exposure or on posting-up of printed matters inproximity to a copying machine, resulting in remarkable deterioration ofthe image quality, and difficulty in decipherment in test ofwater-spilling.

An ink is disclosed which has ejection stability, water resistance ofimages, and other properties improved by introducing at least onespecific structural unit into a dye structure in Japanese PatentApplication Laid-Open No. 1-135880. Further, a recording liquid of blackcolor is disclosed, in Japanese Patent Application Laid-Open No.1-193375, which has high affinity to recording mediums, and superior infixability and water-resistance, giving satisfactory quality of printedletters on an ordinary paper. Furthermore, a recording liquid isdisclosed which is improved in ejection stability, and light fastness ofimages in Japanese Patent Publication No. 62-010274.

The ink is required firstly to have suitability for an employedrecording system, and secondly is required to give satisfactoryproperties of printed matters such as quality and fastness of theimages. However, it is considerably difficult to satisfy simultaneouslyall of the aforementioned various requirements on performances, asunderstood from the prior art disclosures cited above.

The quality of the printed letters mostly depends on a liquid medium ofthe ink, although it depends secondarily on properties of the dyeitself.

The fastness of the printed matter is directly influenced by the dyeproperties. In particular, light-fastness is the most important of thefastnesses, and improvement of the light-fastness has been tried asdescribed above.

Another problem is discoloration or color change which has not beennoticed but has come to be noticed lately as a consequence of technicalprogress. The discoloration is especially serious in black ink which isused in a large quantity. In full color images, the image qualitydeteriorates rapidly by the discoloration.

The discoloration proceeds indoors also without direct sunlightillumination. The discoloration further depends on the kind of arecording medium for forming images thereon, being remarkable on papercontaining silica or the like as a pigment. The widely used C.I. FoodBlack 2 is not free from this problem.

Dyes having satisfactory light-fastness have been sought in order toavoid the disadvantage of C.I. Food Black 2. Consequently, dyes havebeen found that are satisfactory for use on ordinary paper. However,even the ink causing fewer problems on ordinary paper discolorssignificantly on coated paper that has an ink-receiving layer formed ona substrate and containing a pigment and a binder for the purpose ofimproving image quality such as color-developing property of the dyes,sharpness, and resolution. Thus the problem is not solved by merelyemploying a light-fast dye.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a black ink which hasthe above generally required properties and provides no discoloration ofthe image even on coated paper.

Another object of the present invention is to provide an ink-jetrecording method and an apparatus employing the ink.

According to an aspect of the present invention, there is provided anink containing a recording agent and a liquid medium for dissolution ordispersion thereof, the recording agent being a compound represented bythe general formula ##STR3## wherein R¹ and R² are respectively aradical selected from the group of lower alkyl, lower alkoxy, --NHCOCH₃,--COOM, and --SO₃ M; R³, R⁴, and R⁵ are respectively a radical selectedfrom the group of hydrogen, hydroxyl, lower alkyl, lower alkoxy, amino,--SO₃ M, and --COOM; A is ##STR4## R⁶ and R⁷ are respectively a radicalselected from the group of hydrogen, hydroxyl, and lower alkoxy; m is 1or 2; n is 0 or 1; and M is alkali metal or ammonium.

According to another aspect of the present invention, there is providedan ink-jet recording method for conducting recording by ejecting inkdroplets through an orifice onto a recording medium in response to arecording signal, wherein the abovementioned ink is employed.

According to still another aspect of the present invention, there isprovided a recording unit having an ink container portion for holding anink and a head portion for ejecting the ink in droplets, wherein theabove-mentioned ink is employed.

According to a further aspect of the present invention, there isprovided an ink cartridge having an ink container portion for holding anink, wherein the above-mentioned ink is employed.

According to a still further aspect of the present invention, there isprovided an ink-jet recording apparatus having an ink container portionfor holding an ink and a head portion for ejecting the ink in droplets,wherein the above-mentioned ink is employed.

According to a still further aspect of the present invention, there isprovided an ink-jet recording apparatus having a head portion forejecting an ink in droplets, an ink cartridge having an ink containerportion for holding the ink, and an ink-supplying portion for supplyingthe ink from the ink cartridge to the recording head, wherein theabovementioned ink is employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are respectively a longitudinal cross-sectional viewand a lateral cross-sectional view of a head portion of an ink-jetrecording apparatus.

FIG. 2 is an oblique appearance view of a multiple form of the head ofFIG. 1.

FIG. 3 is an oblique view of an ink-jet recording apparatus.

FIG. 4 is a longitudinal cross-sectional view of an ink cartridge.

FIG. 5 is an oblique view of a recording unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described in more detail by reference topreferred embodiment.

The dyes employed in the present invention are generally a sodium saltof a water-solubility-imparting radical such as sulfonic acid radical orthe like. The dye in the present invention, however, is not limited tothe sodium salts. Salts of potassium, lithium, ammonium, and organicamines such as alcohol amine also give the similar effect, which areincluded in the present invention.

Specific examples of the dyes represented by the general formula (I)above are shown below. ##STR5##

The dyes above are produced by a procedure below.

SYNTHESIS EXAMPLE 1

The Exemplified dye No. 1 is synthesized by a conventional manner asdescribed in "Theory and Production in Dye Chemistry" written by YutakaHOSODA as below.

1-amino-2-ethoxynaphthalene-6-sulfonic acid is diazotized in aconventional manner, and is coupled with J acid at a pH range of from 8to 9. The product is further diazotized by sodium nitrite and is coupledwith dimethoxyaniline. The resulting product is still further diazotizedwith sodium nitrite. The diazotized solution is added to a neutralaqueous solution of 1-amino-2-methoxybenzene-5-sulfonic acid, andstirred for 4 hours. The resulting dye is salted out by addition ofsodium chloride and is collected by filtration. Impurities areeliminated from the product by repetition of dissolution, salting-out,and filtration. Thereafter the product is desalted and purified by meansof an ultrafiltration apparatus (made by Sartorius GmbH) to obtain theExemplified dye No. 1.

SYNTHESIS EXAMPLE 2

The sodium salt type of the Exemplified dye No. 4 is synthesized byrepetition of diazotization and coupling reactions in a similar manneras in Synthesis example 1. Subsequently, the sulfonic moieties in thedye molecule are converted to free acid form by means of a stronglyacidic ion exchange resin, and then the acid groups are neutralized withmonoethanolamine to obtain the Exemplified dye No. 4.

The amount of the aforementioned dye to be used in the ink of thepresent invention is generally within the range of from 0.1 to 15% byweight, preferably 0.5 to 10% by weight, still more preferably from 0.5to 6% by weight of the total weight of the ink, although the amount isnot specially limited thereto.

A suitable aqueous medium for the ink of the present invention is water,or a mixed solvent composed of water and a water-soluble organicsolvent.

The water to be used is preferably deionized water, and not ordinarywater containing various ions.

Suitable water-soluble organic solvents to be mixed with water includealcohols having 1 to 5 carbons such as methyl alcohol, ethyl alcohol,n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol,tert-butyl alcohol, isobutyl alcohol, n-pentanol, etc.; amides such asdimethylformamide, dimethylacetamide, etc.; ketones and ketoalcoholssuch as acetone, diacetone alcohol, etc.; cyclic ethers such as dioxane,etc.; polyalkylene glycols such as polyethylene glycol, polypropyleneglycol, etc.; alkylene glycols having alkylene group of 2 to 6 carbonssuch as ethylene glycol, propylene glycol, butylene glycol, triethyleneglycol, 1,2,6-hexane triol, thiodiglycol, hexylene glycol, diethyleneglycol, etc.; glycerin; lower alkyl ethers of a polyhydric alcohol suchas ethylene glycol monomethyl (or monoethyl) ether, diethylene glycolmonomethyl (or monoethyl) ether, triethylene glycol monomethyl (ormonoethyl) ether, etc.; lower alkyl diethers of a polyhydric alcoholsuch as triethylene glycol dimethyl (or diethyl) ether, tetraethyleneglycol dimethyl (or diethyl) ether, etc.; sulfolane,N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and the like.

A suitable organic solvent is selected and used from the above solventsand the like. In particular, glycerin or a polyethylene oxide of apolymerization degree of 3 to 6 is preferable for prevention of cloggingwith ink; a nitrogen-containing cyclic compound or an ether compound ofa polyalkylene oxide is preferable in view of image density and inkejection stability; and use of a lower alkyl alcohol or a surfactant ispreferable in view of frequency responsiveness. Accordingly, thepreferable composition of the solvent in the present invention containsa main component as above in addition to water.

The content of the above water-soluble organic solvent in the ink isgenerally in the range of from 2 to 80% by weight, preferably from 3 to70% by weight, still more preferably from 4 to 60% by weight of thetotal weight of the ink.

The amount of water to be used is generally in the range of from 10 to97.5% by weight, preferably not less than 35% by weight, still morepreferably not less than 45% by weight of the total weight of the ink.At a less amount of the water, a low-volatile organic solvent remains ina formed image, which undesirably causes problems of migration of thedye, running or feathering of the formed image.

The ink of the present invention may optionally contain a pH-adjustingagent, a viscosity-adjusting agent, a surface tension-adjusting agent,or the like in addition to the components described above. ThepH-adjusting agent includes amines such as diethanolamine,triethanolamine, etc.; inorganic alkali salts including hydroxides suchas sodium hydroxide, lithium hydroxide, potassium hydroxide, etc.;organic acid salts such as lithium acetate, etc.; organic acids, mineralacids, and the like.

The ink of the present invention desirably has properties of a viscosityat 25° C. within the range of from 1 to 20 cps, preferably from 1 to 15cps; a surface tension of not less than 30 dyn/cm, preferably not lessthan 40 dyn/cm; and pH within the range of from 4 to 10.

As the recording method for the ink of the present invention, effectiveis an ink-jet recording system. As the recording medium therefor, coatedpaper is effective to obtain an image with high sharpness and highresolution.

The recording medium used in the present invention may be any of mediumsincluding general-purpose ordinary paper (e.g., wood-free paper,medium-quality paper, and bond paper), coated paper, plastic OHP films,and the like. In particular, use of coated paper will achieveconsiderable effects. The coated paper, which is generally constructedfrom wood-free paper as the base material and an ink-receiving layerformed thereon composed of a pigment and a binder, includes in thepresent invention such paper having an ink receiving layer in whichpaper fibers of the base material exist mixedly in the ink-receivinglayer.

The ink of the present invention is especially suitable for an ink-jetrecording method wherein ink is ejected by bubbling of ink caused bythermal energy, because the ink has the characteristics of exceedinglyhigh stability of ink ejection and non-occurrence of a satellite dot.For this use, thermal properties of the ink is sometimes adjusted (e.g.,specific heat, thermal expansion coefficient, thermal conductivity,etc.).

The ink of the present invention, which is particularly suitably for anink-jet recording method for recording by ejecting ink droplets bythermal energy, is naturally useful also for general writing utensils.

The methods and the apparatus suitable for the use of the ink of thepresent invention are those that provide thermal energy to ink in a cellin a recording head in correspondence with recording signals to formliquid droplets by the thermal energy.

An example of the constitution of the heads, which is a main portion ofthe apparatus, is shown in FIG. 1A, FIG. 1B, and FIG. 2.

A head 13 is formed by bonding a plate of glass, ceramics, or plasticshaving a groove 14 with a heat-generating head 15. (The type of the headis not limited to the one shown in the figure.) The heat-generating head15 is constituted of a protection layer 16 formed of silicon oxide orthe like, aluminum electrodes 17-1 and 17-2, a heat-generatingresistance layer 18 formed of nichrome or the like, a heat accumulationlayer 19, and a substrate plate 20 having a good heat-releasing propertymade of alumina or the like.

Ink 21 reaches the ejection orifice 22 (a fine pore), forming a meniscusby action of pressure P not shown in the figure.

On application of an electric signal to the electrodes 17-1 and 17-2,the region designated by a symbol "n" on the heat-generation head 15generates heat to form a bubble in the ink 21 at the position adjacentthereto. The pressure generated by the bubble pushes out the meniscus 23and ejects the ink 21, as a recording droplets 24, and the ink dropletsfly to a recording medium 25. FIG. 2 illustrates an appearance of amulti-head construction by juxtaposing a multiplicity of heads shown inFIG. 1A. The multi-head is prepared by bonding a glass plate havingmulti-grooves with a heat-generation head 28 similar to the onedescribed in FIG. 1A.

Incidentally, FIG. 1A is a cross-sectional view of the head 13 along anink flow path, and FIG. 1B is a cross-sectional view of the head at theline A-B in FIG. 1A.

FIG. 3 illustrates an example of the ink-jet recording apparatus havingsuch a head mounted therein.

In FIG. 3, a blade 61 as a wiping member is held at one end by ablade-holding member. The blade 61 is placed at a position adjacent tothe recording region of the recording head, and in this example, is heldso as to protrude into the moving path of the recording head. A cap 62is placed at a home position adjacent to the blade 61, and isconstituted such that it moves in the direction perpendicular to themoving direction of the recording head to come into contact with theejection nozzle face to cap the nozzles. An ink absorption member 63 isprovided at a position adjacent to the blade 61, and is held so as toprotrude into the moving path of the recording head in a manner similarto that of the blade 61. The aforementioned blade 61, the cap 62 and theabsorption member 63 constitute an ejection-recovery section 64, and theblade 61 and the absorption member 63 remove water, dust, and the likefrom the ink ejecting nozzle face.

A recording head 65 has an ejection energy generation means forejection, and conducts recording by ejecting ink toward a recordingmedium opposing to the ejection nozzle face. A carriage 66 is providedfor supporting and moving the recording head 65. The carriage 66 isengaged slidably with a guide rod 67. A portion of the carriage 66 isconnected (not shown in the figure) to a belt 69 driven by a motor 68,so that the carriage 66 is movable along the guide rod 67 to therecording region of the recording head and the adjacent region thereto.

The constitution of a paper delivery portion 51 for delivery of arecording medium and a paper delivery roller 52 driven by a motor (notshown in the figure) delivers the recording medium to the positionopposing to the ejecting nozzle face of the recording head, and therecording medium is discharged with the progress of the recording topaper discharge portion provided with paper-discharge rollers 53.

In the above construction, the cap 62 of the ejection-recovery portion64 is out of the moving path of the recording head 65, while the blade61 is made to protrude into the moving path. Therefore, the ejectingnozzle face of the recording head 65 is wiped therewith. The cap 62moves to protrude toward the moving path of the recording head when thecap 62 comes into contact for capping with the ejecting nozzle face ofthe recording head.

At the time when the recording head moves from the home position to therecord-starting position, the cap 62 and the blade 61 are at the sameposition as in the above-mentioned wiping time, so that the ejectionnozzle face of the recording head is wiped also in this movement.

The recording head moves to the home position not only at the end of therecording and at the time of ejection recovery, but also at apredetermined interval during movement for recording in the recordingregion. By such movement, the wiping is conducted.

FIG. 4 illustrates an example of the ink cartridge 45 containing ink tobe supplied through an ink supplying member such as a tube (not shown).The ink container portion 40, for example an ink bag, contains an ink tobe supplied, and has a rubber plug 42 at the tip. By inserting a needle(not shown in the figure) into the plug 42, the ink in the ink containerportion 40 becomes suppliable. An absorption member 44 absorbs wasteink.

The ink container portion preferably has a liquid-contacting face madeof polyolefin, especially polyethylene in the present invention.

The ink-jet recording apparatus used in the present invention is notlimited to the above-mentioned one which has separately a head and anink cartridge. Integration thereof as shown in FIG. 5 may suitably beused.

In FIG. 5, a recording unit 70 houses an ink container portion such asan ink absorption member, and the ink in the ink absorption member isejected from a head 71 having a plurality of orifices. The material forthe ink absorption member is preferably polyurethane in the presentinvention.

Air-communication opening 72 is provided to communicate interior of thecartridge with the open air.

The recording unit 70 may be used in place of the recording head shownin FIG. 3, and is readily mountable to and demountable from the carriage66.

The present invention is described in more detail referring to examplesand comparative examples. The unit "%" in the description is based onweight unless otherwise mentioned. The value of "pH" in the descriptionis a hydrogen ion concentration of a finished recording liquid.

EXAMPLE 1

    ______________________________________                                        Exemplified dye No. 1                                                                             4%                                                        Diethylene glycol  30%                                                        Deionized water    66%                                                        pH 6.5                                                                        ______________________________________                                    

EXAMPLE 2

    ______________________________________                                        Exemplified dye No. 2  3%                                                     Diethylene glycol     20%                                                     Polyethylene glycol   10%                                                     (Average molecular weight: 300)                                               Deionized water       67%                                                     pH 5.1                                                                        ______________________________________                                    

EXAMPLE 3

    ______________________________________                                        Exemplified dye No. 3                                                                             3%                                                        Diethylene glycol  15%                                                        N-methyl-2-pyrrolidone                                                                           15%                                                        Deionized water    67%                                                        pH 8.5                                                                        ______________________________________                                    

EXAMPLE 4

    ______________________________________                                        Exemplified dye No. 4                                                                             2%                                                        Triethylene glycol 28%                                                        Deionized water    70%                                                        pH 9.4                                                                        ______________________________________                                    

EXAMPLE 5

    ______________________________________                                        Exemplified dye No. 5                                                                             3%                                                        Diethylene glycol  20%                                                        Ethyl alcohol       5%                                                        Deionized water    72%                                                        pH 7.3                                                                        ______________________________________                                    

EXAMPLE 6

    ______________________________________                                        Exemplified dye No. 6                                                                             3%                                                        Diethylene glycol  20%                                                        Ethyl alcohol       5%                                                        Deionized water    72%                                                        pH 6.8                                                                        ______________________________________                                    

EXAMPLE 7

    ______________________________________                                        Exemplified dye No. 8                                                                             4%                                                        Diethylene glycol  15%                                                        N-methyl-2-pyrrolidone                                                                           15%                                                        Deionized water    66%                                                        pH 4.9                                                                        ______________________________________                                    

EXAMPLE 8

    ______________________________________                                        Exemplified dye No. 7                                                                             4%                                                        Diethylene glycol  30%                                                        Deionized water    66%                                                        pH 6.3                                                                        ______________________________________                                    

The above-mentioned components were sufficiently mixed and dissolved ina vessel, respectively. The mixtures were filtered under pressure by useof a teflon filter having a pore diameter of 0.22 μm to prepare the inksof the present invention.

The inks above were respectively mounted on an ink-jet printer BJ-130A(made by Canon K. K., nozzle number: 48 nozzles), and solid printing wasconducted in a size of 15 mm×30 mm on the recording mediums A, B, and C.Subsequently, the printed matters were left standing for 120 minutes ina dark chamber containing ozone at a concentration of 3±2 ppm foraccelerating discoloration. The color differences ΔE*ab brought about bythe test were measured (according to JIS S 8730). In every case, theΔE*ab was not more than 10, giving less discoloration, which wassatisfactory.

Recording medium A: Specified paper (coated paper) for ink jet printer(IO-730) made by Sharp Corporation;

Recording medium B: Specified paper (coated paper) for PIXEL PRO made byCanon K. K.);

Recording medium C: Specified paper (coated paper) for Paint Jet made byHewlett Packard Co.

With the above-mentioned ink and printer, the ink was ejected in anamount corresponding to 1000 sheets of printing in A4 size (1500 lettersper sheet), and thereafter printing of alphabets and numerals wasconducted on the Recording medium B. As the results, the quality of theprint was satisfactory without defect such as blurring and chipping ofthe alphabets or numerals.

For comparison, the components below were mixed as in the above Examplesto prepare inks, and employed for solid printing on the Recordingmediums A and B. The printed matter was tested in the aforementionedozone-containing test chamber in the same manner as above. It was foundthat in every case, the value of ΔE*ab was 20 or more, giving highdegree of discoloration.

COMPARATIVE EXAMPLE 1

    ______________________________________                                        C.I. Food Black 2              4%                                              ##STR6##                                                                     Diethylene glycol             30%                                             Deionized water               66%                                             ______________________________________                                    

COMPARATIVE EXAMPLE 2

    ______________________________________                                        C.I. Direct Black 51           3%                                              ##STR7##                                                                     Diethylene glycol             20%                                             Polethylene glycol            10%                                             (Average molecular weight: 300)                                               Deionized water               67%                                             ______________________________________                                    

COMPARATIVE EXAMPLE 3

    ______________________________________                                        C.I. Direct Black 91           3%                                              ##STR8##                                                                     Diethylene glycol             15%                                             N-methyl-2-pyrrolidone        15%                                             Deionized water               67%                                             ______________________________________                                    

The use of the dye represented by the general formula (I) gives an inkwhich has the properties required for printed matters on ordinary paperand also is capable of giving a less discoloring image on coated paper.Further it gives an image of high image quality with high resolution andless discoloration, and having satisfactory fastness properties.

The ink of the present invention exhibits sufficiently theaforementioned characteristics at the neutral range of pH 4 to 10, whichis satisfactory in view of safety because of no need of addition ofstrongly alkaline substance such as described in Japanese PatentApplication Laid-Open No. 56-57862.

Furthermore, the ink of the present invention, even when applied toink-jet recording method which ejects ink by action of thermal energy,can be used stably for long time without forming an adhering matter onthe heater, and does not change its physical properties nor forming nosolid deposit during storage.

What is claimed is:
 1. An ink comprising a recording agent and a liquidmedium for dissolution or dispersion thereof, the recording agent beinga compound represented by the general formula ##STR9## wherein R¹ and R²are respectively a radical selected from the group of lower alkyl, loweralkoxy, --NHCOCH₃, --COOM, and --SO₃ M; R³, R⁴, and R⁵ are respectivelya radical selected from the group of hydrogen, hydroxyl, lower alkyl,lower alkoxy, amino, --SO₃ M, and --COOM; A is ##STR10## R⁶ and R⁷ arerespectively a radical selected from the group of hydrogen, hydroxyl,and lower alkoxy; m is 1 or 2; n is 0 or 1; and M is alkali metal orammonium.
 2. The ink of claim 1, wherein a pH value of the ink is withinthe range of from 4 to
 10. 3. The ink of claim 1, wherein the liquidmedium comprises a mixed solvent of water and a water-soluble organicsolvent.
 4. The ink of claim 3, wherein the water is contained in anamount within the range of from 10 to 97.5% by weight of the totalweight of the ink.
 5. The ink of claim 3, wherein the water-solubleorganic solvent is contained in an amount within the range of from 2 to80% of the total weight of the ink.